Have 2 users editing the same database on development server

Hi,

I have been searching everywhere without finding a decent solution for this: I need to have 2 or more users editing the same WordPress site at the same time and have a merging of their edits in the database. Also, it would be great if this would also include editing of CSS files (or any other file, for that matter).

Please take note that the other user would be a client that I’m building the website for, who has no coding knowledge, so a visual interface is a must.

So it would be something like Git, but extended to the database as well.

Thanks!